Alkali cellulose



Patented Jan. 11, 1939 UNITED STATES PATENT OFFICE Weymouth, Midland,

Mich., assignors to The Dow Chemical Company, Midland, -Mich., a corporation of Michigan No Drawing. Application my 26, 1937, Serial No. 144,962

9 Claims.

This invention relates to a method of producing a finely divided alkali cellulose suitable for employment in etherification reactions.

In the preparation of alkali cellulose adapted to the production of cellulose ethers, it has been the practice to produce a finely divided material by means of conventional shredders, or by subjecting the alkali-impregnated cellulose to violent impacts. These procedures have the disadvantage of requiring. considerable time if a uniformly disintegrated product is to be obtained. They also require the expenditure of large amounts of energy to produce relatively small amounts of shredded or disintegrated alkali cellulose. When operated for shorter periods of time than is required to form a uniformly di- -vided alkali cellulose it has been found almost impossible to produce a homogeneous cellulose ether fromthe alkali cellulose.

The principal physical requirement of an alkali cellulose for use in etherification reactions is that it be sufiiciently finely divided so as to remain suspended in the etheriflcation medium until the reaction is complete.

Among the objects of the present invention is to provide a method whereby alkali cellulose may be converted into substantially uniform small particles adapted to the preparation of uniformly etherified cellulose.

We have now found that alkali cellulose, especially an alkali celulose which has been prepared according to the method disclosed in our co-pending application Serial Number 144,374, filed May 24, 1937, of which this application is a continuation in part, may be converted into small flakes of substantially uniform thickness by com pressing the alkali cellulose and passing it between one or more pairs of differential speed rollers as was also disclosed in our aforesaid co-pending application. In each of these sets of disintegrating rolls, if they are of the same diameter, one roller is caused to rotate at a rate substantially greater than the other. If the members of each set of diffential speed rollers are of different diameters, they may be operated at the same axial speeds and yet accomplish the same disintegrating effect as is produced by rollers of equal diameter operating at different axial speeds. The peripheral speed of one roller is preferably about 30 per cent greater than that of the other.

'In a preferred method of carrying out our invention, an alkali cellulose sheet prepared by immersing a cellulosic material in a bath of liquid alkali, preferably more concentrated than 60 per cent and wherein the alkali is substantially completely absorbed, is passed between a set of compression rollers spaced apart a distance considerably less than the thickness of the alkali cellulose sheet. The alkali cellulose is then led from the compression rollers into our disinte- 5 grating mechanism comprising one or more sets of differential speed rollers spaced apart a distance less than the space existing between the compression rollers. The alkali cellulose is thereby disintegrated due to the scufling or tearing action of the differential speed rollers and we have found the product to be almost invariably in the form of flake-like particles 01 substantially uniform thickness. When, for example, a sheet of alkali cellulose 0.125 inch thick is to be shredded, we have ordinarily passed it between a set of compression rollers spaced apart a distance not substantially greater than 0.06 inch and have then led the compressed sheet of alkali cellulose between differential speed rollers spaced apart from 0.015 to 0.030 inch. The product of such treatment is readily etherified when subjected to the action of such an etherifying agent as ethyl chloride.

It is not essential for the successful operation of our process that the alkali cellulose to be shredded be in sheet form. Any mass of cellulosic fibers which have been converted into alkali cellulose may br passed between differential speed rollers to accomplish satisfactory disintegration. If, for example, a cellulosic fluff has been impregnated with alkali according to one of various methods for the production of alkali cellulose, this mass may be supported in a hopper placed adjacent to a set of differential speed rollers and may be fed therebetween either by gravity feed or with the assistance of a conveyor, e. g. a worm. It has been found the most satisfactory results are obtained if the alkali cellulose to be shredded has been cooled until the temperature thereof is at or very slightly above the freezing point of the alkali solution therein contained, especially when concentrated alkali solutions, e. g. those above about per cent sodium hydroxide, have been employed in the preparation of the alkali cellulose.

Owing to the heat generated during the disintegrating step due to the tearing and scuiling action of our differential speed rollers, it is preferable to cool these rollers internally. It is desirable, when the rollers are so cooled, to provide a scraper blade placed therebelow to remove any alkali cellulose which may tend to adhere to the chilled surface after passing between said rollers. This cooling serves to minimize the II degrading eifect of warm alkali on the cellulose molecule and permits of producing a disintegrated mass of alkali cellulose, the particles of which in cuprammonium hydroxide solution have substantially the same viscosity as had a similar solution prepared from the undisintegrated alkali cellulose mass.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

We, therefore, particularly point out and distinctly claim as our invention:

1. In a process for the preparation of alkali cellulose adapted to the production of cellulose ethers, the step which consists in disintegrating the same by subjecting a mass thereof to the action of differential speed rollers.

2. The process of treating an alkali cellulose to be etherified which comprises passing the same between differential speed rollers.

3. In a process for the preparation of finely divided alkali cellulose adapted to the production of cellulose ethers, the step which consists in passing a sheet thereof between compression rollers and thence between differential speed rollers.

4. In a process for the preparation of finely divided alkali cellulose adapted to the production of cellulose ethers, the step which consists in passing a sheet thereof between compression rollers spaced apart a distance approximately half the thickness of the alkali cellulose sheet and thence between differential speed rollers spaced apart a distance less than the distance between said compression rollers.

5. In a process for the preparation of finely divided alkali cellulose adapted to the production of cellulose ethers, the step which consists in passing the same between diiferential speed rollers cooled to a temperature below the freezing point of the alkali solution contained in said alkali cellulose.

6. In a process for the preparation of a finely divided alkali cellulose adapted to the production of cellulose ethers, the step which consists in passing the same between differential speed rollers spaced apart a distance between about 0.010 and 0.030 inch and cooled to a temperature below the freezing point of the alkali solution contained in said alkali cellulose, one of said rollers rotating with a peripheral speed of about 30 per cent greater than that of the other roller.

7. In a, process for the preparation of a finely v tangentially incident to said sheet, the frictional pull applied on one face thereof being greater than that on the opposite face, the resultant imparted movement being in the original direction of travel of said sheet and more rapid than the original rate of travel thereof, thereby disintegrating the sheet of alkali cellulose into substantially fiat particles of approximately uniform size and thickness.

8. In a process for the preparation of a finely divided alkali cellulose adapted to the production of cellulose ethers, the steps which consist in compressing a sheet of alkali cellulose to approximately one-half its original thickness and subjecting both faces of the sheet simultaneously to a continuously applied frictional pull tangentially incident to said sheet, the frictional pull applied on one face thereof being greater than that on the opposite face, the resultant imparted movement being in the original direction of travel of said sheet and more rapid than the original rate of travel thereof, thereby disintegrating the sheet of alkali cellulose into substantially fiat particles of approximately uniform size and thickness.

9. In a process for the preparation of a finely divided alkali cellulose adapted to the production of cellulose ethers, the step which consists in subjecting both faces of a sheet thereof simultaneously to a continuously applied frictional pull tangentially incident to said sheet, while cooling the sheet to a temperature below the freezing point of the alkali solution contained in said alkali cellulose, the frictional pull applied on one face thereof being greater than that on the opposite face, the resultant imparted movement being in the original direction of travel of said sheet and more rapid than the original rate of travel thereof, thereby disintegrating the sheet of alkali cellulose into substantially flat particles of approximately uniform size and thickness.

WILLIAM R. COLLINGB.

LEE DE PREE. MERRILL H. WEYMOUTH. 

